Finite Element Modal Analysis of Machine Tool Pallet Based on Pro/MECHANICA

I. Introduction

Machine tool supports (such as bed, column, pallet, etc.) are the basic components of the machine tool, which can withstand the force and accommodate various components. The dynamic performance of the support directly affects the precision and production efficiency of the machined workpiece. Therefore, it is required that the machine tool support must have sufficient dynamic and static stiffness.

For a long time, machine tool supports at home and abroad generally use empirical design, but in order to ensure that the machine has good dynamic and static performance, and to reduce its weight as much as possible, it is necessary to carry out precise theoretical calculations. Machine tool supports are complex in structure and no precise method has been found to calculate their dynamic performance. But with the development and widespread application of computing and computer technology, engineers can rely on numerical methods to give approximate, more satisfactory answers. At present, among many methods, the mathematical model of mechanical analysis of mechanical systems with finite elements has become the most important method in theoretical modeling. Although the finite element method is also an approximate calculation method, the calculation accuracy is not very high for some support members with complex structure, stress and damping conditions, but it is still the most effective for calculating the dynamic performance of the support. Methods. At present, it is used to calculate the dynamic performance of the support of general complexity, and it is possible to obtain satisfactory calculation results.

Here, we will use the finite element software developed by PTC in the United States, Pro/MECHANICA to carry out finite element analysis on the carriage in the machine support, calculate the natural frequency and vibration mode of the part, and make necessary preparation for analyzing the surface vibration response of the carriage. It also provides a theoretical basis for the design of support parts such as machine pallets, bed bodies and columns.

Second, the current commonly used finite element analysis software and its characteristics

At present, the finite element analysis of mechanical parts generally uses general finite element analysis software, such as ANSYS, MARC and so on. They have a rich and complete cell library, material model library and solver, and have relatively independent front and back processing modules, which can independently complete multi-disciplinary and multi-domain engineering analysis problems. The disadvantage is that the geometric modeling function in the pre-processing module is not strong enough to complete the modeling of the complex model, thus reducing the credibility of the structural analysis results. Some popular 3D design software has powerful modeling tools for geometric models such as Pro/ENGINEER, UG and CATIA. These 3D design software can perform modeling of some complex geometric models. In order to overcome the shortcomings of the general finite element analysis software modeling function, data conversion between software is generally adopted, that is, accurate three-dimensional modeling is performed by using three-dimensional design software, and the model is read in IGES, DXF or STEP format through a standard data interface. Into the general finite element analysis software, and then through the software for accurate calculations.

In the process of model conversion, there are often some problems. Especially after converting some complex models to finite element software, there will be some problems such as loss of face and line and inability to mesh some features in the model. Therefore, after the model is converted, it takes a lot of time and effort to perform geometric model repair work in the finite element software, which inevitably leads to inconsistency of the model and increases the workload. Although some finite element software has developed a complete data interface, it can accurately import most of the geometric models generated on the CAD platform into the finite element software, but the simultaneous use of the two softwares puts more emphasis on the software and hardware of the design platform. High demands will greatly increase the economic burden of some SMEs.

Through comparative analysis of various finite element software, we found that Pro/MECHANICA can achieve complete seamless integration with Pro/ENGINEER, which can directly use the geometric model generated by Pro/ENGINEER for finite element analysis. Because Pro/ENGINEER has powerful parameterization functions, Pro/MECHANICA can use this advantage to perform sensitivity analysis and optimization design of the model. Specifically, when one or more parameters of the model change within a certain range, an optimal geometric model that satisfies certain design indexes (such as minimum mass, minimum stress, etc.) is solved.

Third, the establishment and calculation of the finite element model of the machine tool carriage

1. Establish a geometric model

The analysis here is the X-direction carriage of a CNC high-speed milling machine. This machine is used for roughing large modulus and large diameter gears. Due to the complexity of the structure of the carriage, Pro/ENGINEER software was used for 3D solid modeling.
The machine tool pallet geometry model established by Pro/ENGINEER software is shown in Figure 1.

Figure 1 Geometric model of the carriage

2. Define material properties

Machine tool pallets are important components in machine tool supports. They must withstand the enormous pressure of the table and workpiece during operation and must have high strength. Therefore, the material is selected as gray cast iron HT250. According to the relevant data, the mass density of HT250 is 7340; the elastic modulus is 1.55e11; the Poisson's ratio is 0.27.

In the menu manager [Parts], click the [Settings] → [Material] command option, and define the above material properties.

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